In recent years, thin film devices containing organic semiconductor materials, such as organic EL devices, organic transistor devices and organic thin film photoelectric conversion devices, have attracted attention and have started to be put in practical use. Among the fundamental physical properties of organic semiconductor materials to be used for these thin film devices, carrier mobility and on/off ratio are important. For example, in organic EL devices, efficient charge transport is required for highly efficient luminescence and driving at a low voltage, and carrier mobility is thus important. In organic transistor devices, carrier mobility and on/off ratio, which directly affect their switching speeds and the performance of a device to be driven, are also important.
Further, it is important that they can be stably driven in the air atmosphere. If stably driven in the air atmosphere, it would make work or operation in an inert atmosphere and sealing or the like unnecessary. Hence, the production processes can be simplified and the cost of equipment necessary for the production can be greatly reduced.
In organic semiconductor materials, as with inorganic semiconductor materials, known conventionally are p-type (hole transport) organic semiconductor materials (hereinafter, referred to as “p-type materials”) and n-type (electron transport) organic semiconductor materials (hereinafter, referred to as “n-type materials”). For example, in order to fabricate a logical circuit such as a CMOS (complementary metal oxide semiconductor), a p-type material and an n-type material have been required.
Many studies on p-type materials have been made so far, and materials which exhibit high performance and are stably driven in the air atmosphere have been reported. In contrast, studies on n-type materials have not so much progressed. Many of the materials which have recently been developed, can be driven only in vacuum, and those capable of being driven stably in the air atmosphere are limited.
Compounds having a quinoid structure are a kind of n-type materials capable of being driven stably in the air atmosphere, and quinoid oligothiophene, quinoid benzodithiophene and the like have been developed (Patent Literatures 1 and 2, and Non Patent Literatures 1 and 2). However, it cannot be said that these compounds have sufficient performance, and the they have not put into commercial use. Therefore, there is a need for a semiconductor material having high mobility and a high on/off ratio.